The present invention is directed to a method and apparatus for the sorting of plastic materials by utilizing a known characteristic in such materials when penetrating electromagnetic radiation is directed at the materials and passes through and/or is reflected from and exhibits differing levels of attenuation at different frequencies. The present method and apparatus provide for the separation of the differing plastic materials from each other according to the amount of radiation passing through and/or reflected from particulate materials.
Those skilled in the art are aware that one of the techniques of recycle sorting various plastic materials such as plastic bottles and other similar containers is to grind the materials into particulate or flake matter generally so as to have a flake size of about an eighth of an inch to perhaps as much as a half an inch in width or diameter. It is likewise well known that in order for the sorting of such materials to be recycled economically, they must be processed at relatively high volumes and with a fairly high accuracy in the identification and/or ejection of contaminant or non-selected material. Accordingly, the sorting of plastics is conventionally done in a conveyor operation wherein the materials to be sorted, whether bottles or flake material, are moved along via the conveyor or similar moving carrier to be irradiated by an electromagnetic energy source, such as at near infrared radiation, and the electromagnetic energy passing through the various irradiated articles is detected by one or more detectors, and according to a preselected scheme of determination and evaluation of relative levels of transmitted or reflected electromagnetic energy, various of the passing articles or material are ejected from the stream. U.S. Pat. Nos. 5,966,217; 5,318,172; 5,260,576; RE536,537; and 5,536,935 illustrate differing systems where the conveying of plastic materials to be sorted pass an electromagnetic radiation source and the detection of rays of reflected or transmitted radiation for the later sorting out of the contaminant material by such as being ejected by a blast of air being projected across the stream of materials in a relevant sector.
Two very common materials used for the manufacture of bottles and similar containers are polyethylene terephthalate, commonly known as PET, and polyvinyl chloride (PVC), two resins which are difficult to distinguish by sight alone. Since the materials are common in the manufacture of various bottles and containers, it is not uncommon for manufacturers of any particular bottle to alternate between the two materials based upon availability of material, further complicating the sorting task. It is essential to distinguish correctly between these particular polymers because the presence of PVC in the remolding process of PET bottles incorporating recycled material, even at very low level of occurrence such as a few parts per million, will destroy the uniformity and utility of the PET material.
A paper by D. M. Scott entitled, xe2x80x9cA Two Color Near-Infrared Sensor for Sorting Recycled Plastic Waste,xe2x80x9d appearing in Measurement ScienceandTechnology, Volume 6 (1995), pages 156-159, describes one approach of using near-infrared radiation in a method and apparatus for sorting of PET and PVC materials. The method and apparatus for sorting the materials in the Scott paper, incorporates a method of sorting which utilizes the known dominant peaks of absorption in PET of 1660 nm and for PVC, 1716 nm. The fact that these wave lengths lie in a relatively transmissive portion of the absorption spectrum of water was reported by Scott to be favorable in that water is a common contaminant on plastic materials being recycled by virtue of their being previously washed or otherwise cleaned of various of the debris and contaminants of the particular containers. Scott reports that PET may be distinguished from PVC by measuring the ratio of the transmission levels of the IR energy through the two materials at the identified peaks, noting that if the polymer is PVC then the ratio will be greater that unity, whereas if the material is PET, the ratio will be less than unity. As further reported by Scott, an additional benefit of the technique of using ratio measurement is that it removes some of the effects of sample thickness. As will be recognized by those skilled in the art, there is a great deal of non-uniformity in thickness and size of plastic materials undergoing a sort process, a characteristic which also carries over to the sorting of such plastics in flake form. This is a well known impediment to the use of this method in the sorting of flake. U.S. Pat. No.5,966,217 to Roe et at, reports an essentially identical method for the sorting of PET from PVC. The ""217 patent describes a similar method and apparatus to the Scott paper for to sorting of PET from PVC as well as other materials such as polyethylene naphthalate (PEN). Both the Scott paper and the ""217 patent illuminate the passing plastic material with a near-infrared wave length of radiation, covering the absorption peaks of approximately 1660 nm and 1716 nm, and receiving either directly or by reflection or a combination thereof of the energy passing through the inspected plastics, the radiation being collected and then split to be analyzed after passing through the respective wavelength filters and detectors respectively passing the energy at or near one or the other of the selected wave lengths. Both these references appear to be directed to the sorting of crushed bottles or containers and neither appear to recognize the importance of a method and system for the sorting of flake materials where it is common that more than one flake may be stacked or bunched so as to obscure or complicate the transmission of the electromagnetic energy and the analysis of the received energy.
An alternative approach to sorting of plastic containers is described in U.S. Pat. No. 5,134,291 wherein the infrared reflected from the plastic article is normalized to 1600 and compared to the absorptive peaks of particular plastics.
Another approach for sorting plastics is described in U.S. Pat. No. 5,675,416 wherein flakes of material are examined (somewhat similar to Scott), however, the analysis is based on examining the birefringence characteristics as opposed to IR transmission on reflection characteristics. U.S. Pat. No. 5,339,962, assigned to the owner of the present application, illustrates apparatus for conveying flakes of plastic materials from an inlet, through an illumination zone to an outlet including ejection of contaminant particles by air blast.
The Scott paper describes utilizing a lens to focus the illuminating IR source on the sample and a gold-plated screen type of beam splitter to separate the transmitted energy into two streams for analysis, including the respective filters, lenses and detectors for the selected wavelengths and the ratioing of their outputs. Patent ""217 utilizes a fiber optic splitter rather than the Scott screen, but otherwise focuses by means of lenses, the IR beam on the sample and the transmitted energy on to the fiber optic faceplate. Patent ""217 also describes the ratioing of the respective wavelengths of energy transmitted through the sample at the absorption peaks of PET and PVC, i.e., 1660 nm and 1720 nm. Other than the slight difference in apparatus for splitting the beam of transmitted energy from the sample to the filters, there is little variance in the method and apparatus for distinguishing the materials. The present invention is directed to method and apparatus which are particularly effective in the sorting of particulate plastics such as PET and PVC in whole container form, however, is also particularly effective at the separating of flake from plastic containers, which is a departure from the prior art.
The present invention encompasses a method of distinguishing at least two plastic materials, having different electromagnetic radiation absorption and penetration characteristics by conveying materials to be distinguished from at least one inlet end toward at least one outlet end through an illumination zone, then illuminating the materials in the illumination zone by a source of electromagnetic radiation. The electromagnetic radiation passes through or is reflected from the illuminated materials, or both, and the subsequent steps include splitting the received electromagnetic radiation into a first stream and a second stream; filtering said first stream to pass a preselected wavelength band, said preselected band including an absorptive peak of the electromagnetic radiation illuminating the first of two plastic materials and a higher electromagnetic energy level of transmission or reflection of the second of the two plastic materials; filtering said second stream to pass a preselected wavelength band which includes a band centered at a wavelength wherein the level of energy passed or reflected by the sample of the second material is about equal to the level electromagnetic transmission or reflection of the second of two plastic materials in the wavelength band passing in said first filtered stream; then measuring the strength of a passed sample of said first passed wavelength band; measuring the strength of a passed sample of said second passed wavelength band; then comparing the respective strengths of said first and second passed wavelength bands.
Another object of the present invention encompasses an apparatus for distinguishing at least two plastic materials having different electromagnetic radiation absorption and penetration characteristics comprising means for conveying materials to be distinguished from at least one inlet end toward at least one outlet end through an illumination zone; means for illuminating the materials in the illumination zone by a source of electromagnetic radiation, the source being disposed adjacent to said materials in the illumination zone; means for receiving the electromagnetic radiation passing through or reflected from the illuminated materials, or both, comprising a fiber optic cable having at least two sets of a plurality of individual fibers for carrying received electromagnetic radiation, the receiving end of said fiber optic cable being disposed adjacent to said illumination zone at a distance sufficient for each fiber of each of sets of fibers to receive substantially the same view as any other of the fibers of the electromagnetic radiation passing through or reflected from said materials, or both; means for splitting the received electromagnetic radiation into a first stream composed of the first set of individual fibers and a second stream composed of the second set of individual fibers; means for filtering said first stream to pass a preselected wavelength band, said preselected band centered on an absorptive peak of the electromagnetic radiation illuminating the first of two plastic materials and exhibiting a higher electromagnetic radiation transmission level of the second of the two plastic materials; means for filtering said second stream to pass a preselected wavelength band said preselected band including a band centered at a wavelength wherein the level of energy passed or reflected by the sample of the second material is about equal to the electromagnetic energy level passed or reflected by the second of two plastic materials in the wavelength band passing in the first filtered stream; means for measuring the strength of the energy of the first passed wavelength band then measuring the strength of the energy of the second passed wavelength band and comparing the respective strengths of the energy passed by the first and second passed wavelength bands.